NASA Studies Potential Fix for Discovery's Heat Shield

HOUSTON - NASA engineers are drawing up plans to remove two strips of filler material jutting out from the heat-resistant tiles the space shuttle Discovery belly should mission managers decide the action is needed to safeguard the orbiter's heat shield, shuttle officials said Sunday.

The potential repair, a first if implemented, could be folded into the last of three planned spacewalks for Discovery's crew on Aug. 3, or even warrant a fourth extravehicular activity (EVA), though it is still undecided whether any action is required, they added.

"The jury is out, at this point, on whether any we'll do anything," said Wayne Hale, NASA's deputy shuttle program manager, during an afternoon briefing at here at Johnson Space Center (JSC). "Just the fact that we know about this situation is something new and completely different."

Hale said the imaging provided by astronauts aboard the International Space Station (ISS) - where Discovery is currently docked - and the shuttle's orbital inspection boom have given flight controllers they're first glimpse of the heat shield protrusions, gap-fillers made of a ceramic fiber cloth. In past shuttle flights, they have only been found after landing, shuttle officials said.

While space shuttles have landed safely numerous times with such protrusions, aerodynamics experts are working to determine how the protruding gap-fillers would affect Discovery's reentry through Earth's atmosphere during its planned Aug. 8 landing.

"We have a team of folks working aggressively on options to make that gap filler safe if we decide it's an issue," said Paul Hill, lead flight director for Discovery's STS-114 mission, adding that a separate team is studying the reentry heating effects involved with leaving the protrusions in place. "We expect to have final results on aeroheating and a decision on whether we need to do anything about the gap fillers on Monday."

The aeroheating results should be among of the last pieces of data NASA needs to give Discovery a clean bill of health. NASA engineers are currently working to complete their analysis of Discovery's wing leading edges to ensure the heat-resistant reinforced carbon carbon panels (RCC) are safe for reentry. Initially projected for completion today, image analysts have asked for an additional day to finish studying data collected by Discovery astronauts during a follow-up inspection, Hale said.

The shuttle's ceramic tiles and thermal blankets were cleared for reentry Saturday, NASA officials said.

"We think Discovery is safe to bring home," NASA's top administrator Michael Griffin said on NBC's "Meet the Press" Sunday. "We have approximately one-sixth the number of scars on this orbiter, by actual count, as compared to the average of the last 113 flights."

During in-flight inspections of Discovery's heat shield, astronauts aboard the International Space Station (ISS) photographed the two gap-fillers sticking out; one about 1.1 inches (2.7 centimeters) out from just behind the nose landing gear and another farther back jutting between six-tenths (1.5 centimeters) to nine-tenths (2.3 centimeters) of an inch into space. The protrusions were not caused by impacts or other damage and have been seen in past shuttle flights, but can cause increased drag during reentry and hotter temperatures just aft of the filler materials, NASA officials said.

A typical shuttle reentry generates temperatures of about 2,300 degrees Fahrenheit along the orbiter's tile-covered underside.

During NASA's STS-73 shuttle flight aboard Columbia in 1995, an errant gap-filler was found jutting from its heat shield after landing, said Steve Poulos, NASA's orbiter projects manager. Measuring about 1.4 inches (3.5 centimeters) unrolled, the gap-filler actually stuck out about 0.6 inches (1.5 centimeters) during the descent, with reentry temperatures for the tile section in that flight were estimated at about 2,700 to 2,800 degrees Fahrenheit, he added.

Hill said that gap filler protrusions from the shuttle's forward tile sections are understood out to about a quarter-inch (0.6 centimeters). Since the largest protrusion seen on Discovery is about an inch long, it warrants the added study, he said.

A spacewalk activity